The invention relates to an electron-optical device having a longitudinal axis, an electron-emitting region located in a first plane transverse to the axis, and an electron target located opposite thereto in a second plane transverse to the axis, said target having first and second orthogonal axes, the device further comprising a plurality of electron grids arranged between the first and second plane along the longitudinal axis, each grid having at least one aperture for passing electrons.
A device of this type is known, for example, from U.S. Pat. No. 4,749,904 (=PHN 11.615). In display tubes the electron target is formed by the phosphor screen. To produce a picture usually the electron beam scans the phosphor screen line by line along lines parallel to the longer axis of the screen (the x-axis), the screen having an y-axis orthogonal to the x-axis).
The known device has an electron emitter of the semiconductor type (referred to as cold cathode) with an annular electron-emitting region, but the invention is not limited to this type of electron emitter and is also suitable for use in directly or indirectly heated thermionic cathodes.
An increasingly important aspect in the use of present-day (display tubes comprising) electron-optical devices is that it should be possible to maintain a uniform spot size upon deflection of the electron beam across the entire electron target (=phosphor screen in a display tube). This is a particularly important aspect in (color) monitor tubes.